Question about incorrect TX power indication in Thetis with Hermes Lite 2

[Martin S.]

Hello everyone,

I am using a Hermes Lite 2 together with Thetis v2.10.3.11. I do not have an external PA connected, so I am only using the HL2’s native RF output (approximately 5 W maximum).

When I press “TUN” in Thetis, the TX meter shows around 45 W output power, which is obviously far too high for the Hermes Lite 2. I understand that this is only a meter indication, not the actual RF power, but I have not found a way to correctly scale or adjust this TX power display.

Unfortunately, I do not currently own a power meter, so I cannot measure the real RF output directly. For now it would already be sufficient if I could adjust the indication to be approximately correct for a 5 W maximum output.

Could someone please explain the correct procedure to calibrate or configure the TX power meter in Thetis for the Hermes Lite 2? Any step-by-step guidance or example settings would be highly appreciated.

Thank you in advance for your support.

Best regards,

Martin, DB3MAR

[Evan Hand]

Are you connected to a dummy load when checking the power out?  A mismatched or missing antenna will yield incorrect results.

73

Evan

AC9TU

[DL1YCF]

Thetis (or whatever software shows the power) needs two machine-specific
constants that convert the raw fwd/rev readings (in the range 0-4095)
to actual values in Watt.

I have no experience with Thetis, but its philosophy is to do no auto-
detection but rather rely on the user having chosen the correct model.

This implies that if you do not have a HL2-specific variant of Thetis,
you cannot expect a correct reading here.



> Am 28.12.2025 um 16:45 schrieb Martin S. <inputmast...@gmail.com>:
>
>

[Martin S.]

Hi Evan and all,

thanks for the replies.

No, I am currently not using a dummy load. I am seeing the ~45 W reading on the Thetis TX power meter when transmitting into my antenna. I understand that the reading is not the real RF output power of the Hermes Lite 2, but since the HL2 can only produce about 5 W, the indicated 45 W is very far off and therefore confusing.

Regarding the Thetis version: I am using the MI0BOT build of Thetis, which should be the specific version for the Hermes Lite 2. In the Thetis setup I have also selected the Hermes Lite 2 as device type, and I am using the HL2 together with the I/O board.

My actual question is:
Even if this is only a calculated indication from forward/reverse samples, there must be a way to manually scale or calibrate the TX power meter so that the reading is at least approximately correct. Right now it is almost an order of magnitude too high.

I currently do not own a standalone RF power meter, but I would like to adjust it as well as possible with the equipment I have. If anyone can explain the correct procedure or point me to where the HL2-specific meter constants are set in Thetis, that would be very helpful.

Thanks again for your assistance.

73,
Martin
DB3MAR

[Stano Arendarik]

Hi Evan and all,

it is quite simple - you need the dummy load - for HF bands could be several power resistors in parallel with final resistance equal to 50 Ohm. Then connect output to this load, set the FM mode with no modulation - the carrier signal only is the clean sinus shape and measure the peak voltage on the dummy load by scope. Then you can simply calculate the real output power on the load. The fine tuning of this output power is possible is Thetis for each band. I made it the same on my Hermes HL2. For such band it is possible to reach even higher power than 5W - in my case roughly up to 10W. 

I hope this could help you.

Best Regards,

73,

Stano OM7ADE.

Dne pondělí 29. prosince 2025 v 11:39:52 UTC+1 uživatel Martin S. napsal:

[Martin S.]

Hi Stano and all,

thank you for the explanation.

I have now checked the PA settings in Thetis and I will attach a few screenshots to this post to show my configuration.

I understand the basic procedure with measuring into a 50 Ω dummy load and then calculating the real RF output. What is still unclear to me is where exactly I need to apply the correction inside Thetis.

In my Thetis version (MI0BOT HL2 build) I can see the following values when I press TUN in FM on 20 m:

So internally Thetis already calculates about 6 W forward power, which looks reasonable for the Hermes Lite 2. However, the TX meter on the main screen still indicates roughly 45 W, and I cannot find any option to select “Cal’d Fwd Power” as the source for that meter.

In PA Settings I can see the “10 Watt Meter Trim” table (1–10 W steps), but I am not completely sure whether this is the correct place to adjust the TX meter scale for the HL2 or how these fields should be filled.

Could you please confirm:

1. Is the 10 Watt Meter Trim table the right way to calibrate the TX meter for the Hermes Lite 2?

2. Should I simply match the meter indication to the Cal’d Fwd Power value shown in the PA Values window?

3. Or is there another setting I am missing?

Screenshots of my PA settings and meter configuration are attached for reference.

Thanks again for your help, it is much appreciated.

73,
Martin
DB3MAR